I use a simple wall clock with a second hand. The dial is large and white so that it is easily seen with the safelight. It is positioned over the trays at eye level.

+1

The battery operated clocks are the most flexible.

One warning though - avoid the clocks with a red second hand, especially if you have red safelights.

Matt

“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2